stagefright: add a 2kb cache for CallbackDataSource.
Without a cache the mediaserver does a lot of small reads which result
in round trips through binder and jni to the app MediaDataSource.
On a Nexus 5 I measured time to first frame from MediaPlayer for
1) 1350kbps h264, and 2) 20480kbps vp8. Without a cache, MediaDataSource
was ~250ms slower than an fd. With a 2kb cache it's 30ms slower for (1)
and 70ms slower for (2).
Change-Id: If1e811db7b853c4f79430603318d4744ac30acb9
diff --git a/media/libstagefright/CallbackDataSource.cpp b/media/libstagefright/CallbackDataSource.cpp
index 2e0745f..41f0175 100644
--- a/media/libstagefright/CallbackDataSource.cpp
+++ b/media/libstagefright/CallbackDataSource.cpp
@@ -70,9 +70,10 @@
if (numRead == 0) {
return totalNumRead;
}
- // Sanity check.
- CHECK((size_t)numRead <= numToRead && numRead >= 0 &&
- (size_t)numRead <= bufferSize);
+ if ((size_t)numRead > numToRead) {
+ return ERROR_OUT_OF_RANGE;
+ }
+ CHECK(numRead >= 0 && (size_t)numRead <= bufferSize);
memcpy(((uint8_t*)data) + totalNumRead, mMemory->pointer(), numRead);
numLeft -= numRead;
totalNumRead += numRead;
@@ -94,4 +95,49 @@
return OK;
}
+TinyCacheSource::TinyCacheSource(const sp<DataSource>& source)
+ : mSource(source), mCachedOffset(0), mCachedSize(0) {
+}
+
+status_t TinyCacheSource::initCheck() const {
+ return mSource->initCheck();
+}
+
+ssize_t TinyCacheSource::readAt(off64_t offset, void* data, size_t size) {
+ if (size >= kCacheSize) {
+ return mSource->readAt(offset, data, size);
+ }
+
+ // Check if the cache satisfies the read.
+ if (offset >= mCachedOffset && offset + size <= mCachedOffset + mCachedSize) {
+ memcpy(data, &mCache[offset - mCachedOffset], size);
+ return size;
+ }
+
+ // Fill the cache and copy to the caller.
+ const ssize_t numRead = mSource->readAt(offset, mCache, kCacheSize);
+ if (numRead <= 0) {
+ return numRead;
+ }
+ if ((size_t)numRead > kCacheSize) {
+ return ERROR_OUT_OF_RANGE;
+ }
+
+ mCachedSize = numRead;
+ mCachedOffset = offset;
+ CHECK(mCachedSize <= kCacheSize && mCachedOffset >= 0);
+ const size_t numToReturn = std::min(size, (size_t)numRead);
+ memcpy(data, mCache, numToReturn);
+
+ return numToReturn;
+}
+
+status_t TinyCacheSource::getSize(off64_t *size) {
+ return mSource->getSize(size);
+}
+
+uint32_t TinyCacheSource::flags() {
+ return mSource->flags();
+}
+
} // namespace android
diff --git a/media/libstagefright/DataSource.cpp b/media/libstagefright/DataSource.cpp
index 6a89154..75ef288 100644
--- a/media/libstagefright/DataSource.cpp
+++ b/media/libstagefright/DataSource.cpp
@@ -283,7 +283,7 @@
}
sp<DataSource> DataSource::CreateFromIDataSource(const sp<IDataSource> &source) {
- return new CallbackDataSource(source);
+ return new TinyCacheSource(new CallbackDataSource(source));
}
String8 DataSource::getMIMEType() const {
diff --git a/media/libstagefright/include/CallbackDataSource.h b/media/libstagefright/include/CallbackDataSource.h
index 678eb2e..1a21dd3 100644
--- a/media/libstagefright/include/CallbackDataSource.h
+++ b/media/libstagefright/include/CallbackDataSource.h
@@ -44,6 +44,36 @@
DISALLOW_EVIL_CONSTRUCTORS(CallbackDataSource);
};
+
+// A caching DataSource that wraps a CallbackDataSource. For reads smaller
+// than kCacheSize it will read up to kCacheSize ahead and cache it.
+// This reduces the number of binder round trips to the IDataSource and has a significant
+// impact on time taken for filetype sniffing and metadata extraction.
+class TinyCacheSource : public DataSource {
+public:
+ TinyCacheSource(const sp<DataSource>& source);
+
+ virtual status_t initCheck() const;
+ virtual ssize_t readAt(off64_t offset, void* data, size_t size);
+ virtual status_t getSize(off64_t* size);
+ virtual uint32_t flags();
+
+private:
+ // 2kb comes from experimenting with the time-to-first-frame from a MediaPlayer
+ // with an in-memory MediaDataSource source on a Nexus 5. Beyond 2kb there was
+ // no improvement.
+ enum {
+ kCacheSize = 2048,
+ };
+
+ sp<DataSource> mSource;
+ uint8_t mCache[kCacheSize];
+ off64_t mCachedOffset;
+ size_t mCachedSize;
+
+ DISALLOW_EVIL_CONSTRUCTORS(TinyCacheSource);
+};
+
}; // namespace android
#endif // ANDROID_CALLBACKDATASOURCE_H